The present invention relates to multipin connectors and more particularly to multipin connectors having soldered connections of wires to individual pin terminals of the connectors enveloped within a heat shrinkable sleeve wherein the heat is developed internally of the sleeve and to the method of making the same.
Flat rectangular, multipin connectors are in extensive use today particularly in the military. In the latter environment it is essential that each termination be sealed against the ambient atmosphere and presently this is accomplished by enclosing each termination (connection of wire to pin terminal) within a sealed tube. Specifically a wire to be connected to a pin termination has its end stripped and a heat shrinkable plastic tube slid over the insulation adjacent the stripped end of the wire. The sleeve has a ring of solder centrally located internally thereof and rings of sealant at each end of the sleeve. The wire is placed on the pin terminal and the sleeve is slid over the insulation of the wire and the other end over the pin beyond the region of overlap of pin and wire.
All wires and sleeves are so positioned and then hot air guns, or equivalent (ovens) are used to heat the structure; see FIG. 7 of U.S. Pat. No. 3,945,114. In U.S. Pat. No. 3,721,749, it is suggested that induction heating can be used but there is no description or discussion of the apparatus or structures required for such operation. Regardless of the heat source used in the operation, the solder melts, the sleeve shrinks and the solder is bought into contact with the region of contact between the wire and pin and the end rings of sealant bond to the adjacent surfaces, providing a sealed connection.
There is a fundamental problem with such a structure and procedure. The heat must be applied through a plastic, the sleeve. The sleeve is a poor conductor of heat and thus the temperature of the hot air external to the sleeve must be much greater than the actual temperature required to melt and flow the solder. This is due to the large temperature drop across the wall of the plastic sleeve. Also the time to produce satisfactory joints is unnecessarily long. Further, when connectors are employed in situations where the wires sizes or lengths vary greatly, and the heat required must be varied in order to accommodate the largest and/or longer wire size, the terminations of smaller and/or shorter wires are subjected to excessive heat and may be damaged. Also during this process the solder may be made overheated and thus degraded, or underheated and thus producing a cold solder joint, and/or the sealant may not be properly heated and thus does not environmentally seal.